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Left-handedness is the preference for the left hand over the right for everyday activities such as writing. Most left- handed people exhibit some degree of ambidexterity. Left-handedness is relatively uncommon; seven to ten percent of the adult population is left-handed. Template:Citation needed

Main article: Handedness

Hand orientation is developed in fetuses, most commonly determined by observing which hand is predominantly held close to the mouth.[2]

In 2007, researchers discovered LRRTM1, the first gene linked to increased odds of being left-handed. Possession of this gene slightly increases the possibility of left-handedness, although genetic predispotion to handedness has not yet been established. [3][4]

Vanishing Twin Theory: This theory postulates that left handed individuals were originally part of an identical twin pair, with the right-handed twin fetus failing to develop early in development. Mirror twins consist of one left handed and one right handed individual. Each twin is in effect a "mirror image" of the other. Such occurances would coincide with the approximate population of left-handed births (10-15%).

Long-term impairment of the right hand: People with long-term impairment of the right hand are more likely to become left-handed, even after their right hand heals.Template:Citation needed Such long-term impairment is defined as eight months or more.

Testosterone: Exposure to higher rates of testosterone before birth can lead to a left-handed child.[5] This is the Geschwind theory, named after the neurologist who proposed it, Norman Geschwind. It suggests that variations in levels of testosterone during pregnancy shape the development of the fetal brain. Testosterone suppresses the growth of the left cerebral hemisphere and so more neurons migrate to the right hemisphereTemplate:Citation needed. The highly developed right hemisphere is now better suited to function as the center of language and handedness. The fetus is more likely to become left-handed, since the right hemisphere controls the left half of the body. The theory goes on to tie the exposure to higher levels of testosterone and the resultant right-hemisphere dominance to auto-immune disorders, learning disorders, dyslexia, and stuttering, as well as increased spatial ability.

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Template:Off-topic There are many colloquial terms used to refer to a left-handed person, e.g. "southpaw" or "goofy". Some are just slang or jargon words, while other references may be offensive or demeaning, either in context or in origin (e.g. the British "cack-handed"). In more technical contexts, 'sinistral' may be used in place of 'left-handed' and 'sinistrality' in place of 'left-handedness'. Both of these technical terms derive from sinestra, a Latin word meaning 'left'. Left hand shakes are a sign of disrespect - however the left hand shake is the standard in the international Scouting movement. In Hebrew, as well as in other ancient Semitic and Mesopotamian languages, the term "left" was a symbol of power or custody. The left hand symbolized the power to shame society, and was used as a metaphor for misfortune, natural evil, or punishment from the gods. This metaphor survived ancient culture and was integrated into mainstream Christianity by early Catholic theologians as Ambrose of Milan to modern Protestant theologians such as Karl Barth to attribute natural evil to God in explaining God's omnipotence over the universe.

Meanings gradually developed from use of these terms in the ancient languages. In many European languages, "right" is not only a synonym for correctness, but also stands for authority and justice: German recht, French droit, Spanish derecho, Portuguese direito; in most Slavic languages the root prav is used in words carrying meanings of correctness or justice. The right hand has also historically been associated with skill: the Latin word for right-handed is dexter, as in dexterity; indeed, the Spanish term diestro and the Italian's destro, mean both "right-handed" and "skillful". In Irish, "deas" means "right side" and "nice". "Ciotóg" is the left hand and is related to "ciotach" meaning "awkward"; in French, "gauche" means "left" and is also a synonym of "maladroit", meaning "clumsy". Same for the Italian "maldestro" (literally "bad right" or "not right" with the term right here used as opposed to left and not to wrong) and the Dutch word "links".

Meanwhile, the English word sinister comes from the Latin word sinestra, which originally meant "left" but took on meanings of "evil" or "unlucky" by the Classical Latin era. Alternatively, sinister comes from the Latin word sinus meaning "pocket": a traditional Roman toga had only one pocket, located on the left side. The contemporary Italian word sinistra has both meanings of sinister and left (the masculine adjective for sinister being sinistro). The Spanish siniestra has both, too, although the 'left' meaning is less common and is usually expressed by izquierda, a Basque word that made its way into Portuguese too. In Portuguese, the most common word for left-handed person, canhoto, was once used to identify the devil, and canhestro, a related word, means "clumsy" ( sinistro means only "sinister"). Furthermore, in English, the expression "To have two left feet" refers to clumsiness in the domains of football or dancing.

The left side is often associated with awkwardness and clumsiness. The English expression "having two left feet", the Dutch expression " twee linkerhanden hebben", the Spanish expression " tener dos pies izquierdos", the German expression " zwei linke Hände haben", the Bulgarian expression " dve levi ratse", the French expression " avoir deux mains gauches" and the Czech expression " Mít obě ruce levé" ("to have two left hands") all mean being clumsy. Moreover, the German idiom " mit dem linken Fuß aufgestanden sein", the Spanish expression " levantarse con el pie izquierdo" and the french one " s'être levé du pied gauche" (literally, to have gotten up with the left foot) means to have a bad day and do everything wrong or unsuccessfully (like "to get out of the wrong side of the bed" in English).

In ancient China, the left has been the "bad" side. The adjective "left" (Chinese character: Template:Lang, Mandarin: zuǒ) means "improper" or "out of accord". For instance, the phrase "left path" (Template:Lang, Mandarin: zuǒdao) stands for illegal or immoral means. The pictograph for "left", Template:Lang depicts a left hand attending to work. In contrast, the pictograph for "right", Template:Lang (Mandarin: yòu) depicts a right hand in relation to the mouth, suggesting the act of eating. Contrast this pattern with the Muslim example below. At the same time, in modern Chinese conscience the left is firmly held as the dominant and "male" side, epitomized in the formula "man-left, woman-right".

In Welsh, the word chwith means left, but can also mean strange, awkward, or wrong. The phrase tu chwith allan (left side out) refers to an object being inside-out.[12]

In some Spanish-speaking countries, to do something por izquierda means to engage in corrupt conduct or employ illegitimate means; whereas por derecha or a derechas means to do it the right (legitimate) way.[13]

In Dutch, "twee linkerhanden hebben" (having two left hands) means that one is clumsy or is a very poor handyman. The English equivalent of the phrase is "being all thumbs".

In Finnish, the word oikea means both right (okay, correct) and right (the opposite of left).

In Hungarian, the word for right is jobb which also means better. The word for left is bal, and is used in expressions such as kétbalkezes ("having two left hands"), balszerencse (bad luck), bal lábbal kel fel ("get up (from bed) with the left leg", an omen that predicts a bad day coming up).

In Swedish, vänster means left. The term vänsterprassel means infidelity, adultery; cheating. From this term the verb vänstra (lit. "lefting") is derived.

In Ireland left handedness is called a "ciotógach" (kitt-OHG-och) which is the Irish language term for left-handed. It is frequently used amongst Irish people, e.g. "she gave him a slap of the ciotógach after he insulted her at the bar" the word ciotógach is not derogatory and is held with affection amongst left-handed people.

The Scots term for left-handedness is corrie fistit. The term can be used to convey clumsiness.

In some parts of the English-speaking world 'cack-handed' is slang for left-handed (it is also used to mean clumsy). The origin of this term is disputed, but some suggest it is derived from the Latin cacare, in reference to the habit of performing ablutions with the left hand, leaving the right hand 'clean'. However, other source suggest that it is derived from the Old Norse word keikr, meaning "bent backwards" Australians frequently use "cacky-handed". A less common Australian slang word for a left-handed individual is the term Molly-Dooker, whose origins cannot be ascertained for certain.

Amongst Muslims, and in some societies including Nepal and India, it is customary to use the left hand for cleaning oneself with water after defecating. The right hand is commonly known in contradistinction from the left, as the hand used for eating.

Even the word " ambidexterity" reflects the bias. Its intended meaning is, "skillful on both sides". However, since it keeps the Latin root "dexter", which means "right", it ends up conveying the idea of being "right-handed at both sides". This bias is also apparent in the lesser-known antonym "ambisinistrous", which means "clumsy on both sides" and derives from the Latin root "sinister", which means "left".

Among Incas left-handers were called (and now are called among the indigenous peoples of the Andes) lloq'e ( Template:Lang-qu) which has positive value. Peoples of the Andes consider that left-handers possess special spiritual abilities, including magic and healing. Third Sapa Inca - Lloque Yupanqui - was the left-hander, his name in transfer with Quechua means "the glorified lefthander".

In tantras Buddhist, the left hand represents the wisdom.

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A left-handed individual may be known as a southpaw, particularly in a sports context. It is widely accepted that the term originated in the United States, in the game of baseball. Ballparks are often designed so that batters are facing east, so that the afternoon or evening sun does not shine in their eyes. This means that left-handed pitchers are throwing with their south-side arm. The Oxford English Dictionary lists a non-baseball citation for "south paw", meaning a punch with the left hand, as early as 1848, just three years after the first organized baseball game, with the note "(orig. U.S., in Baseball)."

In boxing, someone who boxes left-handed is frequently referred to as southpaw. The term is also used to refer to a stance in which the boxer places the right foot in front of the left, so it is possible for a right-handed boxer to box with a southpaw stance. Most boxers, southpaw or otherwise, tend to train with sparring partners who adopt an orthodox stance which gives southpaws an advantage. Manny Pacquiao is an example of a southpaw (although he writes with his right hand). In the popular boxing film series Rocky, the main character Rocky Balboa is a 'southpaw'.

Southpaw is also a term in professional wrestling, often giving them the advantage.

In tennis, southpaws hold the racket in their left hand. Because of this, their grip of the handle is supposedly adjusted in a slightly different style from right-handed players. Some world champion left-handed tennis players include Jimmy Connors, John McEnroe, Martina Navratilova, Marcelo Ríos, and Rafael Nadal.

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Left-handed people are sometimes placed at a disadvantage by the prevalence of right-handed tools in society. Many tools and devices are designed to be comfortably used with the right hand. For example, (right-handed) scissors, a very common tool, are arranged so that the line being cut along can be seen by a right-handed user, but is obscured to a left-handed user. Furthermore, the handles are often molded in a way that is difficult for a left-hander to hold, and extensive use in such cases can lead to varying levels of discomfort. Most importantly, the scissoring or shearing action - how the blades work together (how they are attached at the pivot) - operates correctly for a right-hander, but a left-hander will tend to force the blades apart rather than shearing the target substance. So-called ambidextrous scissors do not help, since the cutting blades are still set right-handed.

Input devices for computers can present obstacles for the left-handed when optimized for the right. Some computer installations have the computer mouse placed on the right side of the keyboard and unable to be reposition to the left. The mouse itself is also sometimes shaped to fit the right hand better. Other input devices such as trackballs and trackpads can be positioned in such a way that they are difficult for left-handed. These may also have two buttons that, while functionally reversible, are sized for the convenience of the right-handed person.

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While European-style kitchen knives are symmetrical, Japanese kitchen knives have the cutting edge ground asymmetrically, with ratios ranging from 70-30 for the average chef's knife, to 90-10 for professional sushi chef knives; left-handed models are rare, and usually must be specially ordered or custom made.

Left-handed scissors require inverting both the handles and the blades if the left-handed user is to fully see the progress of the cut. Right-handed scissors place the thumb's blade on the left side, while left-handed scissors have this on the right side. This ensures the left hand's motion draws the blades together while cutting, ensuring a cleaner cut.

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Left-handed adaptations have even bridged the world of music; guitars are often made especially for left-handers, though generally at a higher cost, and with greatly reduced availability ( Jimi Hendrix was known to use a right-handed guitar flipped around to play left-handed). There have even been inverted pianos where the deepest notes correspond to the rightmost keys instead of the leftmost. Inverted trumpets are made, too, but at a considerably higher cost. Although the trumpet's valves are normally designed to be operated with the right hand, the prevailing belief is that left-handed trumpeters aren't at a significant disadvantage. The French horn, for example, is played with the left hand, yet most horn players are right-handed.

Left-handed golf clubs were one of the earlier, and well-accepted, manifestations of a special version of an implement; the most notable left-handed-playing participant being Phil Mickelson (he is naturally right-handed).

Other items which are inconvenient for left-handers include train-station turnstiles, can openers, circular saws, potato peelers, corkscrews, rulers, number keys on keyboards, watches, chequebooks, spiral notebooks, boomerangs, measuring cups and pencil sharpeners.

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It can be difficult for left-handed children to learn to write if the teacher does not take the student's left-handedness into account. In fact, even in the later 20th century, some UK schools were discouraging children from writing with their left hand, often seriously affecting the child's development ( Hansard 1998). When properly done, left-handed writing is a mirror image to that of the right-hander, making the teaching process confusing for the right-handed teacher of a left-handed student. Some chairs are equipped with writing boards on the right side only, contributing to this behavior. The result is that left-handed students learn to write with their hand curled around the pen so that it can meet the paper at the same angle as the right-hander and also to account for the front page of notebooks and binders, as the books open so you write on the right side, which puts the binding on the left side, inhibiting the left hand from writing freely. Once this habit is formed, it is difficult to break. This curling of the hand results in the heel of the palm being placed behind the writing, forcing the writer to lift it off the paper and making the grip even more awkward. In addition, constantly lifting and replacing the hand over fresh ink often causes smudging, causing problems for many left-handed students, especially in exam situations. When the left hand is held correctly, it is below the writing, as is typical for right-handers.

Left-handed people who speak Arabic, Persian, Urdu, Hebrew or any other right-to-left language do not have the same difficulties with writing. The right-to-left nature of these languages prevents left-handers from running their hand on the ink as happens with left to right languages. However, because these alphabets were developed for right-handed people, the characters are still often more easily matched to a right-handed profile.

Left-handers also have an advantage in learning 19th-Century copperplate hands, which control line-width by pressure on the point, because the proper angle for the pen point is slanted "northeast," which puts the right hand in an awkward, "crabbed" position. Some pen makers make bent nibs to allow right-handers to point the pen in the direction that allows the best control.

The vast majority of firearms are designed for right-handed shooters, with the operating handle, magazine release, and/or safety mechanisms set up for manipulation by the right hand, and fired cartridge cases ejected to the right. Also, scopes and sights may be mounted in such a way as to require the shooter to place the rifle against the right shoulder. A left-handed shooter must either purchase a left-handed or ambidextrous firearm (which are manufactured in smaller numbers and are generally more expensive and/or harder to obtain), shoot a right-handed gun left-handed (which presents certain difficulties, such as the controls being improperly located for them or hot shell cases being ejected towards their body, especially their eyes or down their collar or right sleeve), or learn to shoot right-handed (which may be less comfortable or "natural" for them). A related issue is ocular dominance, due to which left-handed people may wish to shoot right-handed, and vice versa.

Some modern firearms are ambidextrous (e.g. the FN P90 and Heckler & Koch P7), or can be converted between right- and left-handed operation (e.g. the Heckler & Koch G36 and Steyr AUG). Bullpup rifles are particularly problematic for left-handers unless they can be reconfigured, since empty shells would be ejected straight into the shooter's face and cheek potentially causing injury. The British LA-85 Assault Rifle must be fired right-handed, placing left-handed soldiers at a disadvantage; this policy does however mean that any soldier can pick up and immediately fire a fallen comrade's gun without checking its configuration and potentially needing to convert it. In contrast the Steyr AUG is of a modular design, and the ejection port and extractor can be switched/replaced to suit the handedness of the soldier operating it. The M-16 and its variants have a fixed ejection port, but being a conventional (i.e. not bullpup) design the ejection port is forward of the operator and hence able to be fired either handed. Circa 1980, with the introduction of the M16A2 version, a case deflector was incorporated adjacent to the ejector port to direct discarded shells in a more forward direction, making the rifle even more left hand operator friendly. The deflector is not always effective, however, as the ejected shell still stands a chance of hitting the left-handed shooter's cheek, especially in windy conditions.

Lever action and pump action firearms present fewer difficulties for left-handers than bolt action weapons do. Many weapons with adjustable sights allow for left-handed use, but a right eye dominant shooter is necessary to adjust. In fact, most weapons adjust well enough that a weapon will not eject shells into a left-hander's eye.

One of the few cameras ever produced for left-handers was the half-frame Yashica Samurai. Cameras predominantly have the hand grip, shutter release, film wind lever and commonly used selection buttons, switches and dials controlled by the right hand, lens controls (where present) tend to be accessible by either hand. When a left-handed person uses a right-handed camera the hand control can be less steady and hence produce camera shake leading to poorer pictures at low shutter speeds.

Most guitars are designed to be played right-handed (that is to say the right hand is used to strum or pick the strings while the left hand manipulates the fret board). Although a right-handed guitar may be converted for left-handed playing (as was most notably done by Jimi Hendrix, Paul McCartney, Tony Iommi and Kurt Cobain), this always requires replacing the bridge and nut for the strings to fit and the intonation to be correct. This "quick alternative" to getting a "real" left-handed guitar has only been necessary due to a considerable lack of true left-handed instruments, manufactured specifically for the left-handed player. Many guitar brands make left-handed versions of their popular products.

In his book Right-Hand, Left-Hand, Chris McManus of University College London argues that the proportion of left-handers is rising and left-handed people as a group have historically produced an above-average quota of high achievers. He says that left-handers' brains are structured differently in a way that widens their range of abilities, and the genes that determine left-handedness also govern development of the language centres of the brain.

McManus also says that the increase in the 20th century of people identifying as left-handed could produce a corresponding intellectual advance and a leap in the number of mathematical, sporting, or artistic geniuses.

In 2006, researchers at Lafayette College and Johns Hopkins University in a study found that left-handed men are 15 percent richer than right-handed men for those who attended college, and 26 percent richer if they graduated. The wage difference remains unexplained, and does not appear to apply to women.

Main article: Handedness of Presidents of the United States

Most left-handers draw figures facing to the right.

There is a high tendency in twins for one to be left-handed

Stuttering and dyslexia occur more often in left-handers (particularly if they are forced to change their writing hand as a child, like King of England George VI).

Left-handers adjust more readily to seeing underwater.

Left-handers excel particularly in tennis, baseball, swimming and fencing

Left-handers usually reach puberty 4 to 5 months after right-handers

4 of the 5 original designers of the Macintosh computer were left-handed

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Lefties Have The Advantage In Adversarial Situations, ScienceDaily, April 14, 2006.

Science Creative Quarterly's overview of some of the genetic underpinnings of left-handedness

Quirks & Quarks June 10, 2006 (CBC radio documentary on left-handedness including interviews with four scientists holding different views on the determinants of handedness)

A left-handed senior citizen recalls the emotional torment he faced at a New York public school in the 1920s. (Audio slideshow)

Famous Left-Handers

Woznicki, Katrina (2005). "Breast Cancer Risk Doubles for Southpaw Women", MedPage Today, 26 September.

Hansard (1998) 'Left-handed Children', Debate contribution by the Rt Hon. Mr. Peter Luff (MP for Mid-Worcestershire), House of Commons, 22 July.

A 1918 Popular Science Monthly article on left-handedness -- Is your Child Left-Handed? Why, according to psychological tests, left-handed people ought to remain so, Popular Science monthly, December 1918, page 22, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA22

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Left-handedness is the preference for the left hand over the right for everyday activities such as writing.

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There are dozens of left-handers worldwide. They use their other hand for stuff and everything.